Approximately 1-2% of the United States population has epilepsy. Most epilepsy is well-controlled with the available anticonvulsant agents. Approximately 20% (250,000 in the United States), however, have medically refractory (i.e. intractable) epilepsy. While surgical treatment of intractable epilepsy has been gaining in acceptance and use, comprehensive assessments of outcomes are lacking. As pointed out during the NIH Consensus Development Conference on Epilepsy Surgery, there is a fundamental lack of reliable information concerning the effects of surgery, not just on seizure control but on quality of life, and specifically whether seizure control is accompanied by improvements in quality of life. To make rational recommendations and decisions regarding the use of epilepsy surgery, one needs definitive and comprehensive information regarding the risks and benefits of surgery. The following proposal is for a unique, prospective, multi-center, longitudinal study of approximately 400 patients who will undergo resective surgery for relief of medically intractable seizures. To accrue an adequate sample size, patients will be recruited from six centers in the Northeast. Patients will be prospectively recruited and followed from the beginning of the presurgical evaluation to at least two years after surgery. The primary goals of the study are 1) to determine the probability and predictors of entering a one-year remission (i.e. no seizures for one year) within two years after surgery; 2) to determine the magnitude of change from presurgical baseline in quality of life and in productive activity at 3 months, 1 year and two years after surgery, and to determine how much change can be expected as a function of change in seizure frequency, seizure severity, and decrease in medications; 3) to determine the magnitude and nature of changes in cognitive function post- versus presurgery; and 4) to document psychiatric and neurologic complications. We also propose to conduct methodologic work on health-related quality (HRQOL) assessment for epilepsy surgery, using data that will be collected already for the primary study goals. These analyses include refinement of a recently developed seizure-based outcome system so that its outcome categories maximally reflect HRQOL after epilepsy surgery, comparison of the measurement properties of three HRQOL measures (SF-36, ESI-55, and QOLIE- 89) In study patients, and development and evaluation of Spanish language versions of these HRQOL measures. The proposed study represents a unique, multi-center effort that will result in the largest systematic study of epilepsy surgery to date and will provide definitive answers to key questions regarding the outcomes of epilepsy surgery, as well as their measurement.